The invention relates to a method of constructing a tunnel or underpass beneath an existing construction, and more particularly to a method of tunneling a railroad underpass without disrupting or requring change in existing track construction, and without interrupting railroad service on the tracks.
Often times it is desired for both safety and convenience to establish a pathway or roadway over, through or under an existing structure. In order to do so, it has been necessary to disrupt the existing structure. For example, should it be desired to build a roadway over or under a set of railroad tracks, the use of the tracks is interrupted for the duration of construction, or at least for long intervals, to permit construction of a bridge over or an underpass beneath the tracks. Service must be halted.
Another approach, useable only in some locations, is to provide alternative, temporary routing for the railroad tracks, called a run around. However, such approach requires availability of adjacent land for placement of the alternative roadbed or run around; at least temporary disruption of use of the tracks when the connection and disconnection of the temporary tracks is made; and continued interruptions and delays in service while trains traverse the temporary tracks, inasmuch as the run around is not usually built to the same standards as the permanent tracks and contains fairly sharp curves. More important, the acquisition of land and construction and removal of the temporary tracks adds greatly to the expense of constructing the bridge tunnel or underpass. In fact, many needed underpasses are not constructed because disruption of use of the railroad is not tolerable, and insufficient funding is available for construction of both the underpass and the run around.
While it has been suggested before that a tunnel could be constructed beneath railroad tracks without disruption of service, see for example U.S. Pat. Nos. 3,438,208 and 3,631,680, the methods and techniques suggested required in-ground placement of extremely large bodies, unconventional and esoteric construction methods, and elaborate, specialized equipment not available to general construction contractors. The proposals simply were not feasible or practical. Construction of run arounds would be far less costly.